Trade: By exchanging trade goods with your opponents,
you are actually receiving needed resources that will increase your
total income while improving your relations with the race that you
are trading with. As long as you are not actively engaged in a war
with a race, you will be able to trade with them.

By signing a trade treaty, you agree to exchange a specified amount
each year, up to 25% of the lesser player’s production total.
Both players then receive a percentage return based on the number
of years the treaty has been established.

Since establishing trade requires an initial investment for organizing
patrolled trade routes and establishing customs, your income from
a trade treaty begins at –30% of the treaty amount. Each turn
thereafter, your trade income increases by +0–5%, so you usually
do not generate a positive income until after 10–12 years.
The trade revenues are then divided up among your planets in proportion
to their productions. Your income percentage continues to increase
until it reaches a maximum of 100% of the treaty amount. Humans
get an additional +25% on all trade returns.

For example, you could control two planets that have a combined
production total of 500 BC while your neighbor has three planets
with a production total of 400 BC. The maximum that you could trade
would then be 100 BC per turn (25% of your neighbor’s production).
You both agree to exchange the maximum. After twenty turns the percentage
return has reached 25%, indicating that you and your neighbor are
making a profit of 25 BC per turn from the trade. The profits are
distributed proportionally among your planets. If one of your planets
was producing 200 BC per year and the other 300 BC per year, the
first would receive 10 BC trade profit and the second 15 BC profit.

If an already existing treaty is in effect, the percentage return
begins as the average of your current return and –30%. This
new return rate is then applied to the new treaty amount. For example,
you have a trade agreement for 100 BC per year, currently at a 50%
return rate and you establish a new agreement for 200 BC a year.
The percentage return becomes 10% (the average of 50% and –30%),
applied to the new treaty amount of 200 BC, generating a trade income
of 20 BC. The return rate continues to grow again at +0–5%
per turn, until reaching 100% of the new amount.